Subterranean drilling systems that employ downhole drilling motors are commonly used for drilling boreholes in the earth for oil and gas exploration and production. A subterranean drilling system typically includes a downhole drilling motor that is operably connected to an output shaft. Bearing apparatuses (e.g., thrust, radial, tapered, and other types of bearings) also may be operably coupled to the downhole drilling motor. A rotary drill bit configured to engage a subterranean formation and drill a borehole is connected to the output shaft. As the borehole is drilled with the rotary drill bit, pipe sections may be connected to the subterranean drilling system to form a drill string capable of progressively drilling the borehole to a greater depth within the earth.
A typical bearing apparatus includes a stator that does not rotate and a rotor that is attached to the output shaft and rotates with the output shaft. The stator and rotor each includes a plurality of bearing elements, which may be fabricated from polycrystalline diamond compacts (“PDCs”) that provide diamond bearing surfaces that bear against each other during use.
The operational lifetime of the bearing apparatuses often determines the useful life of the subterranean drilling system. Therefore, manufacturers and users of subterranean drilling systems continue to seek improved bearing apparatuses to extend the useful life of such bearing apparatuses.